Why can't people figure out warp versus runout versus disc thickness variation

Why, for Christs' sake, can't people figure out the difference in the
English language between warp versus runout or disc thickness variation?
There has been a perennial argument since the 70's when someone got the
notion that brake rotor (aka disc) "warp" is the same as "dtv" (which it's
not), where it can't be shaken out of their heads that they are two
completely different things. Likewise with "runout".
Witness this reference posted in good faith to the home-repair group today:

Which referenced this paper:

The Effect of Residual Stress on the Distortion of Gray Iron Brake Disks
In that paper, the Asian authors *continually* appear to callously abuse
the English language by confusing the term "warp" with "disk thickness
variation (DTV)", which is completely different from warp (as in a potato).
For example, you can have a warped sheet of metal where the thickness
variation is zero, and you can have a thickness variation without warp.
If this was a high-school kid equating the two, I'd shrug it off as
ignorance; but this is an engineering paper, for heaven's sake.
Here is the first sentence where they appear to abuse the English language:
"It is known that disk warping or uneven disk thicknesses
induce pulsation during brake applications."
Clearly it is well known that "warp" (as in potato) and "uneven thickness"
are two completely different things - which means that this particular set
of Asian authors (M. W. ShinG. H. JangJ. K. KimH. Y. KimHo Jang) are likely
ignorant of what "warp" actually means - or - they simply assume that it
means something that it doesn't mean (i.e., warp and thickness variation
are completely different things - they just are).
They then compound their abuse of the English language in a sentence not
far from that last horrid sentence, saying:
"When the disk temperature is increased by friction heat during braking,
the heat often causes dimensional instability of the disk,
permanently modifying the runout or disk thickness variation (DTV)
of a disk and producing brake judder."
This sentence clearly appears to indicate the authors have no clue how to
use the English language because it's a fact that runout and DTV are also
two completely different things.
============ terms below ==============
Stop the ?Warped? Rotors Myth and Service Brakes the Right Way
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BTW, if you skim the paper, these two definitions may be useful:
Gray Iron

"pig or cast iron containing much graphitic carbon which causes
its fracture to be dark gray"
Residual Stress
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"Residual stresses are stresses that remain in a solid material after the original cause of the stresses has been removed."
Reply to
Arlen Holder
To be sure of their meaning, you will need to be fluent in Korean and read the original paper in its native language, Korean.
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Reply to
Paul in Houston TX
I'm not sure the paper is actually written originally in Korean, are you?
The authors seem completely ignorant that the word "warp" has two different meanings, one of which is the colloquial abuse of the word, while the other is the technical use of the word.
Given that it's a technical paper, I'm astounded that they used the colloquial term, and even more so astounded that we can assume that's a peer reviewed paper, where one wonders how it got accepted given the horrid abuse of the English language.
Given the paper equated "warp" with DTV & lateral runout, this description is apropos to describe what those two latter terms mean, technically speaking: Stop the ??Warped?? Rotors Myth and Service Brakes the Right Way Where that author advises: "Starting today, remove ??warped rotor?? from your vocabulary. Instead, you should be both looking for and educating your customers about these terms: Lateral Runout & Disc Thickness Variation (DTV)"
Reply to
Arlen Holder
Odds are the authors are not fluent in English and they had a grad student translate for them. There is no telling what they orginally meant.
"The Effect of Residual Stress on the Distortion of Gray Iron Brake Disks"
Authors Authors and affiliations
M. W. Shin G. H. Jang J. K. Kim H. Y. Kim Ho JangEmail author
M. W. Shin 1 G. H. Jang 1 J. K. Kim 2 H. Y. Kim 2 Ho Jang 1 Email author
1.Department of Materials Science and EngineeringKorea UniversitySeoulRepublic of Korea 2.R&D DivisionHyundai Motor Company and Kia Motors CorporationHwaseong-siRepublic of Korea
Reply to
Paul in Houston TX
Are you assuming that the 'or' means they are equating 'warping' with 'thickness variations'? Maybe they just mean that either condition can cause pulsations.
Again, maybe they mean that 'dimensional instability' can modify either runout or DTV, causing brake judder, without equating the two distiortions.
Reply to
I fully agree that the "or" is confusing in and of itself, but I read the entire paper, so I know what they *measured*, where they did NOT measure warp.
Warp is easily measured since anyone who checks a head, for example, measures it for warp. You use a known-straight surface and then you use feeler gauges to see the variation in "flatness" to that known flat surface.
From the word "or", I agree with you the authors' intent is ambiguous - but from their measurements, they clearly measured DTV and lateral runout.
I think they intended on proving that *heat treating* caused less lateral runout and/or less disc thickness variation - which I'm sure they did accomplish.
But that's not the same thing as warp, which is not only the word they used repeatedly, but which was the reason that the person referred me to that paper, since *he* thought the paper had something to do with warp.
It didn't. It just used the word. But they abused the English language in using the word (IMHO).
That boggles the mind that people are _that_ sloppy using that technical term, particularly because disc rotors can't warp (as in potato chip) because the temperatures required are impossible to achieve according to the reliable references I've seen.
Raybestos says: "Brake rotors do not warp from heat..."
This says: "Rotors are cast in extreme heat three to five times greater than the most aggressive braking situation. Physically, warping a rotor would require a similar application of extreme heat, which is impossible."
This says: "...the temperature required to make metal that resilient soft enough to simply bend would be tremendous."
This says that there are adverse effects starting at 1200dF: "When this local temperature reaches around 1200 or 1300 degrees F. the cast iron under the deposit begins to transform into cementite (an iron carbide in which three atoms of iron combine with one atom of carbon). Cementite is very hard, very abrasive and is a poor heat sink. If severe use continues the system will enter a self-defeating spiral - the amount and depth of the cementite increases with increasing temperature and so does the brake roughness."
This says: "in more than 40 years of professional racing, including the Shelby/Ford GT 40s, one of the most intense brake development program in history - I have never seen a warped brake disc."
These say the myth of warped rotors started in the 1970's:
This non-scientific thread, which we can quickly assume isn't scientific so let's just take it as a reasonable point of view only, says that the surface may get to 600dF but the rest of the rotor is at a lower temperature than the surface.
It's pretty clear from this (and other references) that the authors abused the term "warp" - but since the long term solution for a warped rotor is completely different than the long term solution for a rotor with lateral runout or disc thickness variation, it's *important* the distinction.
NOTE: A compounding factor is that the short-term solution to warp is the *same* for disc-thickness variation (but not for lateral runout) - which is why you consistently get guys implementing the short term solution for brake judder instead of the long-term solution, simply because they *think* their rotors warped (as in potato chip).
Hence, use of the wrong terminology has many dollars of unintended consequences (likely hundreds of millions of wasted money every year, IMHO).
Reply to
Arlen Holder
[Followups set to a group that might find this interesting.]

Bad translations by non-native speakers will always be with us. When you're using a language that's not your own, it's not always easy to find le mot juste.
Using the wrong technical term in a technical paper is a problem, of course, but it hardly amounts to an abuse of the English language.
Now, if the disk had capsized, ...
Reply to
Peter Moylan
I bought a 97 Contour in 2001, and it had brake pulsation. I called it warped rotor, not caring much what was the precise distortion that caused the pulsation. I replaced all four rotors myself for $105. Not really big money. It's been a long-term solution: I still keep the car for pulling a trailer, and the problem has never returned. Maybe they weren't 'warped', or maybe they were, by careless lug nut tightening.
Another sort of physics/language problem -
"Rotors are cast in extreme heat three to five times greater than the most aggressive braking situation."
I don't think it makes sense to speak of multiples of temperature unless you are referencing to absolute zero.
Reply to
Agreed that the abuse of the word "warp" has zero negative effects ... if ... if ... if ... if ... if .... if ... if ... if ... if...
Remember the Spartan's response to the "if we attack you" diplomatic 'cable' way back in the days of the Greeks? The keyword is if.
If you actually *act* on "warp", you'll do the most insane things, and, in the end, you'll *still* have your vibration.
Thats' because the long-term solution for warp is *different* than the long term solution for, say, lateral runout or disc thickness variation.
The short term solution is the same - but the long term solution is completely different.
That's the main reason it matters.
Reply to
Arlen Holder
It doesn't matter what you call it. The fix is still the same. My guess is that the warping problem is caused by hard braking and the resulting transf er of friction material from the pads to the rotor surface. This occurs on a molecular level and results in the rotor surface acquiring areas of diffe ring friction coefficients. This can cause hot spots on the rotor when brak ing. To that effect, I try not to clamp down too hard on the brakes after c oming to a stop when going down a hill. That's pretty the only thing that c an be done to protect your rotors.
Reply to
I acted on "warp", sensibly replaced my rotors, and it solved the problem permanently.
Reply to
Two things commonly happen:
1. Something goes wrong with your suspension causing a slight shimmy. Maybe a ball joint is loose, maybe a rod is bent. As you brake, the shimmy causes the pressure on the rotor to change and soon a "warp" is worn into the rotor surface.
2. Someone tensions your lug nuts without using a torque wrench. Maybe they use torque sticks and are sloppy, maybe they do it by hand with a maltese cross and a hammer. Uneven pressure is placed on the rotor, and the same uneven wear pattern results. If you're really lucky, your lugs break off too.
Avoiding these two situations will cause your brake rotors to last much longer. --scott
Reply to
Scott Dorsey

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